a) Field of the Invention
The present invention relates to an electromagnetic valve having a magnetic core member secured to a housing and a method for manufacturing the same. The electromagnetic valve is suitably applicable to a vehicular internal combustion engine for controlling a fuel supply quantity or controlling a purge quantity of an evaporated fuel into an intake air system of the engine.
b) Description of the Related Art
In general, for example, a purge system of an evaporated fuel has been adopted in a vehicular internal combustion engine in which a fuel gas evaporated in a fuel tank (so-called, an evaporated gas) is temporarily reserved into a canister and the evaporated gas is introduced into an intake air passage to burn the evaporated gas with the intake air so that the evaporated gas is prevented from being discharged into the atmosphere external to the engine. In the purge system, a purge passage is installed between the canister and intake air passage for causing the evaporated gas to be circulated into the intake air passage, in a midway through the purge passage an electromagnetic valve such as a purge control valve being installed so as to enable an open or closure of the purge passage according to a drive signal inputted thereto.
A previously proposed structure of the electromagnetic valve such as the purge control valve will be described below.
A valve casing formed in a stepped cylindrical shape includes: a core inserting hole through which a core member as will be described below is inserted; and a valve seat arranged for seating a valve body (which will be described below) thereon, both of the core inserting hole and the valve seat being coaxially and vertically extended in the electromagnetic valve. In addition, inlet and outlet are projected radially from the valve casing, both of the inlet and outlet being mutually communicated or interrupted according to an open and closure of the valve seat. An annular metallic plate made of a magnetic material is buried into an internal (thickness portion) of the valve casing so as to enclose the valve body. A part of the annular metallic plate is projected radially from the valve casing.
An approximately letter-U shaped housing formed of the magnetic material such as the iron member or a magnetic stainless steel material is positioned on an outer periphery of the valve casing and extended in the axial direction of the valve casing.
A core inserting hole at a basic end of the housing is placed on an axis line of the valve casing so as to be coaxial with the core inserting hole of the valve casing. A tip end of the approximately letter-U shaped housing is linked to the annular metallic plate.
A rod-shaped core member made of the magnetic material such as iron or magnetic stainless steel includes: a large diameter portion inserted into a core inserting hole of the valve casing; a small diameter portion located on a basic end of the large diameter portion and inserted into a core member attaching hole of the housing at a position projected from the core inserting hole; and a diameter extended portion formed on a basic end of the small diameter portion.
It is noted that the core member is secured to the core member inserting hole of the housing through the diameter extended portion and is extended along the axial line of the core member attaching hole.
In addition, the core member is attached onto the valve casing together with the housing and its large diameter portion is coaxially extended within the core member inserting hole of the valve casing. A tip end of the large diameter portion is faced against a valve body with a constant clearance to limit a lift distance of the valve body (a valve opening variable of the valve body) at a predetermined magnitude. An electromagnetic coil is located on an outer periphery of the core member inserting hole and is buried into an internal of the valve casing. The electromagnetic coil is energized by an external power supply to form a magnetic field thereabout to open a valve body.
The valve body is made of the magnetic material of an iron system metal and is installed within the valve casing. The valve body is attracted magnetically onto the core member by means of the power supplied electromagnetic coil so as to be separated from a valve seat of the valve casing to open the valve.
When the electromagnetic coil receives the power supply, a closed magnetic path is formed with the coil, plate, housing, the core member, and the valve body is magnetically attracted onto the tip end of the core member (large diameter portion). Hence, the valve body is open and is contracted on the tip end of the core member so as to communicate the inlet with the outlet.
In addition, when the electromagnetic valve is assembled, the electromagnetic coil and the valve body are at first attached onto the valve casing, the core member is fixed onto the housing, and, thereafter, the housing is attached onto the valve casing.
It is noted that when the core member is fixed onto the valve casing, with the large diameter portion of the core member is attached onto a clamp, after the small diameter portion is inserted within the core member attaching hole, a pressurizing jig such as a punch is used to apply the pressure onto the basic end of the small diameter extended portion. Hence, the diameter extended portion is deformed due to a plastic deformation on the small diameter portion. Consequently, the core member cannot be drawn out from the housing by means of the diameter extended portion.